This invention relates generally to rotary shaft seals. More particularly, it relates to an improved rotary shaft seal designed to provide positive-contact sealing when at rest and gap-type operation when rotated. The invention is a result of a contract with the United States Department of Energy.
Plate-type rotary shaft seals are known which are designed to operate with a clearance when rotated and to provide positive-contact sealing at rest. For example, U.S. Pat. No. 3,782,737 (L. Ludwig; Jan. 1, 1974) and U.S. Pat. No. 3,499,653 (J. Gardner; Mar. 10, 1970) describe spiral-groove viscoseals designed to provide positive sealing in the static mode and a gas-containing running clearance during operation. Both of those seals are subject to the disadvantage that some rubbing of the seal plates occur at startup and shutdown. U.S. Pat. No. 3,685,839 (A. Frei; Aug. 22, 1972) describes a hydrostatic seal having an axially movable, non-rotatable member which is biased toward a rotatable member. At startup, when the system pressure is below a selected value, a pressure-responsive piston assembly moves the axially movable member away from the rotatable member. When that pressure exceeds the selected value, the piston assembly is deactivated, permitting the non-rotatable member to move somewhat closer to the rotatable member. In general, conventional positive-clearance sealing devices are subject to the disadvantage that they are speed-dependent, pressure-dependent, or temperature-dependent to a significant extent.
U.S. Pat. No. 3,725,986 (L. Hoogenboom; Apr. 10, 1973) relates to power transducers of the piezoelectric type and to a method for mounting the elements thereof so as to achieve high transmission efficiency between the transducer and its supporting body. U.S. Pat. No. 3,657,581 (L. Hoogenboom; Apr. 18, 1972) disclosed a squeeze-film damper bearing utilizing a plurality of piezoelectric or magnetostrictive transducers to impart transverse oscillatory motion to one of the confronting surfaces of the bearing. An acoustic horn is used to couple the transducers to the bearing surface to be oscillated, with the result that the maximum axial movement of the surface is about 200 times the value of the thickness excursions of the crystal. These patents to Hoogenboom are incorporated herein by reference. U.S. Pat. No. 3,359,045 (S. Hsu; Dec. 19, 1967) discloses a squeeze-film bearing in which a tubular piezoelectric transducer is one of the bearing surfaces. U.S. Pat. No. 3,351,393 (C. Emmerich) describes the use of a pair of oppositely polarized piezoelectric discs which are energized alternately to oscillate an annular bearing mounted on a shaft. U.S. Pat. No. 3,471,205 (J. Farron et al) discloses a squeeze-film bearing in which a rotatable shaft is journaled on a layer of compressed air located on the inner surface of a piezoelectric member encircling the shaft.